1. Field of the Invention
This invention pertains to a packet exchange and a stored program controlled switching system, and more particularly to a call information matching system for matching information on calls in call processors in the packet exchange when a severed communcations link is restored.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional stored program controlled-switching system (SPCS).
A stored program controlled switching system (SPCS) has a plurality of processors which handle the calls. An SPCS shown in FIGS. 1 & 2 comprises a line concentrator (LC), a digital switching module (DSM), a call processor (CPR) and a main processor (MPR). The line concentrator (LC) directly terminates plural pieces of terminal equipment (TE), multiplexes and transmits cells to intraoffice highways, performs a scan and signal distribution (SCN/SD) call control from each piece of the terminal equipment (TE) on a time slot sixteen (TS16) for an analog subscriber, and extracts D channel call control information for a digital subscriber. The switching module (DSM) switches a data frame, e.g. a packet or a cell, over to output highways. The call processor (CPR) performs a call control by commanding the switching digital module (DSM), based on call control information from the line concentrator (LC). The main processor (MPR) controls the entire exchange system and its communications with other offices.
For example, an eight megabit per second [8 Mbps] optical communications link connects the most subordinate processor with a subscriber loop carrier shelf (SLCSH) for accommodating an analog subscriber, having thirty-two [32] time slots every two megabits per second [2 Mbps]. A change in the scan and signal distribution call control (SCN/SD) detected by the hardware is notified as TS16 information to the most subordinate processor for its processing.
The line concentrator (LC) shown in FIG. 1 comprises a digital loop carrier shelf (DLCSH) for accommodating a digital subscriber, a subscriber loop carrier shelf (SLCSH) for accommodating an analog subscriber, a digital terminal shelf (DTSH) for accommodating a digital terminal, a signal controller (SGC) for exchanging TS16 data or D channel call control information, a line switch (LSW) for switching over to the signal controller (SGC) various input/output data from the digital loop carrier shelf (DLCSH), the subscriber loop carrier shelf (SLCSH) and the digital terminal shelf (DTSH), and a line processor (LPR) for supervising the line switch (LSW) and the signal controller (SGC).
In case of a digital loop carrier shelf (DLCSH), a D channel is one of time slots zero [0] (TSO), which is a time slot in an eight megabits per second (8 Mbps) optical communications link, as a link control access protocol for a D channel link (LAPD link) for use in a call processing control.
FIG. 2 is a sketch outlining a processor control by a stored program controlled-switching system (SPCS).
As described above, the line processor (LPR) controls communications with the terminal equipment (TE), the call processor (CPR) controls stored program communications and other services (such as numerical translations and connections), and the main processor (MPR) controls the switching system (SPCS).
It is still possible that statuses of calls controlled by these processors, do not match each other, when the processors resume a phase-B/C or when a communications link between the processors is restored. To overcome such a possibility, the prior art system is arranged such that the processors for call processing temporarily suspend all of their monitoring functions for matching calls on completion of a phase-B/C resumption or a communications link restoration, and then restart respective monitoring functions for detecting a subscriber action (e.g. an OFF-HOOK event and an ON-HOOK event) on completion of a matching process for preserving a call.
A phase resumption is to invoke a system initialization caused by a hardware fault or a software fault related to an intra-processor CC control. B/C refers to a severity of a fault.
FIG. 3 is a sequence diagram illustrating a conventional call preservation process.
More specifically, FIG. 3 shows in detail the procedure outlined in the description of FIG. 2.
Both, a superordinate processor (e.g. a call processor or a CPR) and a subordinate processor (e.g. a line processor or LPR) cover an interruption thereby ignoring a request for processing a subscriber action. Then, the superordinate processor creates lists of calls to be preserved and notifies the subordinate processor of the lists of the calls to be preserved. Each list itemizes a plurality of calls to be preserved. The subordinate processor determines whether or not a call in the list can be preserved by its own information items or pieces and notifies the superordinate processor of the determination in a matching result response.
After repeating the procedure for all the lists of calls to be preserved, both the superordinate processor and the subordinate processor initialize calls not to be preserved, thereby completing a call matching for preserving a call. Then, they announce a resumption of a call processing and restart respective monitoring functions.
However, a conventional call preservation process requires a considerable amount of time for matching call information held by the respective processors in addition to time required for communications between them. Currently, it requires about one [1] to two [2] minutes. Meantime, a subscriber action, such as a call origination, generated during the call preservation is completely blocked. The reason why the respective processors suspend their monitoring functions for all calls generated during the call preservation process through an exchange of lists of calls to be preserved between them is that the next process cannot be phased in by responding to a subscriber action without having a call preservation between the respective processors.
That is, the prior art has a problem that a user cannot expect a normal service immediately after a completion of a communications link restoration or a phase-B/C resumption, due to lack of response for a subscriber action such as a call origination.